Yes, Rick. That's exactly what I do. Once the propellant has reached casting
temp, I pour the whole thing into the casing with nozzle already installed and
plugged (to avoid spillage). I have a 3 foot 1inch diameter aluminum rod that
is guided down the center of the pipe by a coupler and reducer on top with a 8
inch long 1 inch pvc pipe that the aluminum rod slides smoothly down. This
ensures a perfectly centered core. Once inserted, the aluminum rod rests on a
chamfer in the convergent side of the nozzle on one end and exits the opposite
end centered thru the coupling/reducer/pipe fitting. It is left alone for 3
hours, and then twisted loose with channel locks. The plug is removed from the
nozzle and the entire length of the core is carefully examined with an indirect
light from both ends. Due to the viscosity inherent in flexi-fuel, I usually
end up with a perfectly smooth core.
Having said that, I think Richard is spot on. In my attempt to improve my Isp
of the propellant (which usually ranges from 95 -100 Isp), I came up with a
mixing method I call "IMM" or "intimate mixing method". It involves 1.
Grinding the KNO3 in a coffee grinder in SMALLER batches in order to reduce
particle size2. Drying the entire batch of KNO3 (in this case, 625 gram batch
KNO3) for 30 minutes at 275F3. Combining with the powdered Su (in this case
173 grams no need to grind) in a ziploc bag4. Tumbling SMALL 200 gram batches
in tumbler for 2 hours.5. Vacuum sealing the batches as they finish
tumbling.6. Once all batches have been tumbled, combine them all in zIploc and
cook them to casting temp.7. Pour entire contents down the casing in one
viscous pour.
This IMM method produced consistent Isp of 110 - 114. And therein lies the
rub. Because the batches are so intimately mixed, the end product was not as
viscous as I had obtained with the less mixed batches and lower Isp. The
finished product with the IMM was more like soupy mashed potato. The point is
that IT DID NOT POUR SO EASILY AND I HAD TO SCOOP IT IN. I think this really
sets the grain up for possible and even unavoidable voids or cracks. So I
obtained higher Isp than even Pollino reported but at the cost of lower
viscocity and, as a result, probable voids in the grain. THIS NO DOUBT WOULD
EXPLAIN THE SPIKE IN THRUST. Having said that, I checked this grain with light
and the core looked perfect with no cracks or voids. Nonetheless, I should've
checked density.
So, it looks like it's going to have to be a compromise. I'll have to settle
for lesser Isp in order to obtain a more viscous product to not only pour
easier but more importantly, fill in any possible voids or cracks. AND CHECK
DENSITY!!
As a side note, I will say that incorporating IMM in KNDX has given me
consistent 125 -130 Isp. with no issues.
Tad
-----Original Message-----
From: Rick Maschek <dmarc-noreply@xxxxxxxxxxxxx>
To: sugpro@xxxxxxxxxxxxx <sugpro@xxxxxxxxxxxxx>
Sent: Fri, Nov 20, 2020 2:25 pm
Subject: [sugpro] Re: Near cato...what happened?
How are you making the core? Casting with a mandrel or drilling or ? I wonder
if sliding a bright LED light down the core in a dark room would yield any
voids visually if the light penetrates both propellant and pvc case.
As for debonding with the pvc case, do you do any case prep prior to pouring in
the propellant?
On Friday, November 20, 2020, 11:15:18 AM PST, Rick Maschek
<dmarc-noreply@xxxxxxxxxxxxx> wrote:
Your motor is a progressive motor right? Doesn't that mean pressure and
thrust increase until it either burns out or CATOs?
If the thrust (and pressure) is increasing more than the single grain sims
shows and no evidence of nozzle blockage, that means increase of Kn more than
expected. If you are case bonding by pouring in the flex fuel you are not able
to visually check the grain so as Richard indicated, checking your density very
accurately might help. Since you don't know what 100% density should be of the
propellant you cast, I would also mix more than you need and cast a solid plug
that you can determine what your density should be with the propellant cast in
the motor.
I've heard of people saying their density was over 100% that leads me to
believe they are not measuring carefully or doing something else wrong and when
you are measuring small amounts, a small error in measuring makes a large %
error. If I'm off by a millimeter in one of my 4, 6, 8, or 12" grains that
amount is insignificant. I've never reached 99% with any of my grains.
Rick
On Friday, November 20, 2020, 10:16:39 AM PST,
<dmarc-noreply@xxxxxxxxxxxxx> wrote:
Bill, Nope. Right here in the US. Used Christy's PVC cement and primer
Tad
-----Original Message-----
From: Bill Kuker <bkuker@xxxxxxxxxxxxx>
To: SugPro <sugpro@xxxxxxxxxxxxx>
Sent: Fri, Nov 20, 2020 11:39 am
Subject: [sugpro] Re: Near cato...what happened?
That is very similar to what I do for delay, though I swapped to using a
coupler and a reducer instead of drilling an end cap. I also use the method
documented on R. Nakka's site but developed by Chuck Knight if I remember
correctly, of creating a restriction in the 1/2" pvc (rubber bands and boiling
water) so that the delay mixture has positive retention. It looks like you
might do that as well, but it's hard to tell in the "after" photos.
That fissure crack is not something like I've ever seen though. Are you in the
the US / Canada? I've seen "pvc" pipe and cement from other regions of the
world that is very different from what we have here.
On Fri, Nov 20, 2020 at 10:45 AM Redacted sender tadserralt for DMARC
<dmarc-noreply@xxxxxxxxxxxxx> wrote:
Yes, Bill. The white mark is the fissure crack from the burn thru. I think
you're right. I think the delay element was blown thru but I've done this many
other times with the same pressures without incident. I believe it was
compromised due excessive pressure of unknown origin. I'm not sure that
explains why the thrust went so high so quickly. The delay blowing thru does
not appear to me to be the cause but the affect of the pressures inside.
Don't have diagram of delay but it is basically 1/2 inch x 1inch pvc with a 2
gram sample of a 6 gram sample of 70/30 KNSU & 2 gram Epoxy. End cap is
drilled. pvc inserted with collar inside and then covered with anchoring
cement up to delay top.
Tad
-----Original Message-----
From: Bill Kuker <bkuker@xxxxxxxxxxxxx>
To: SugPro <sugpro@xxxxxxxxxxxxx>
Sent: Fri, Nov 20, 2020 10:29 am
Subject: [sugpro] Re: Near cato...what happened?
I can't quite tell, does that white mark on the forward (ejection charge) end
come from a hole where it burned through the pvc joint?
Otherwise it looks to me like the delay burned through way too soon, or perhaps
was blown out, and you had a "nozzle" on each end.
These 4 (image below) frames look like the delay let go, there is also a little
"pop" in the audio that sounds to me like a delay plug or nozzle coming out of
a pvc motor to me (ask how I know ;) ) and then flame A shots out sideways,
being redirected by the wood.
Flame B interests me, is it just flame A redirected again because it's confined
by the wood, or is it from a separate failure point?
I put a lot of stock in the sound, I think an overpressurization usually sounds
more like a rifle shot, and this sounds to me like a normal burn, a pop as the
delay end uncorks, and then a slightly different but not overpressure burn.
Have a diagram of how your delay is constructed?
-Bill
On Fri, Nov 20, 2020 at 10:08 AM Redacted sender tadserralt for DMARC
<dmarc-noreply@xxxxxxxxxxxxx> wrote:
Hello everyone,Below is a link to a video of the latest static test on a
J-Class 2" Diameter, 1" core, 12" single grain pvc motor with a .5625" nozzle.
Kn initial 171 and KN Max and Final at 278. I've had very good success with
this progressive single grain burn using Pollino's Flexi-fuel formula 65/18/17
KNO3/Su/Corn syrup. I've had nominal results with multiple 15 inch 1.25"
diameter single grain I-class motors and a recent successful 24 inch 2"
diameter 1" core single 24 inch grain K-Class PVC motor with a .8125" nozzle
(Kn initial: 155 Kn Max and Final: 279).
https://www.youtube.com/watch?v=h9SMcbwAi5U&feature=youtu.be
So what the hell happened here? This was half the size of the successful
K-Class and I maintained same formulation and a proper Kn profile. It didn't
cato. It just blew the forward closure containing the delay element and burned
right thru a 2 inch wood plank and toasted my scale. All in less than .4
seconds. I considered Overpressurization due to a blockage caused by the epoxy
plug I used in the igniter on one side in order to force the initial burn down
the core. But even then, I would think that over-pressurization due to some
blockage would obviously increase the pressure inside but not increase the
thrust; and yet notice the pounds of thrust. My K-Class had a max thrust of
256 lbs. This J-Class went to more than 340 lbs before it scorched the scale!!
And all of this in less than .4 seconds!! Can a blockage do that? Or maybe a
partial blockage causing smaller throat diameter? Cracked grain increasing
burn rate? I doubt it because that's the whole point of flexi-fuel: very
viscous which allows a single grain pour. What exactly happened? I really
would like to know before proceeding any further. Hoping the footage helps in
figuring it out. Thank you for your kind attention.
Tad